Low voltage lighting systems are well known. Such a system typically includes a power pack or power box which is connected to a 120 VAC source, and a plurality of low voltage (typically 12 VAC) light fixtures connected to the power box via insulated cable. The present invention relates specifically to such power boxes.
The typical low voltage lighting system power box includes a variety of electrical components, e.g., 120 VAC/12 VAC step down transformer, relay, one or more switches, and a photoelectric element, depending on the complexity of the system. The Toro Company, assignee herein, manufactures power boxes of various types and complexity, including those which simply include an on/off switch; those which include a photoelectric element and which turn the lights on at dusk and off at dawn; and those which include a photoelectric cell and a solid state timer which combine to turn the lights on at dusk and off after four or eight hours, as selected. A typical prior art power box base 190 is shown in FIG. 10. The cover is not shown. Base 190 contains a step down transformer 192; a PC board 194 connected to transformer 192; a photocell 196 carried by PC board 194; and a window 197 for photocell 196. A 120 VAC cable 204 and a 12 VAC cable 210 connect to and power the components listed above.
While numerous improvements have been made to low voltage light fixtures to render them more adjustable, less costly, etc., low voltage power boxes have received much less attention. One of the problems with prior low voltage power boxes is the method by which the 120 VAC and 12 VAC cables are connected to the box. A common way to attach the 120 VAC cable to the power box is through the use of a "tortuous path" strain relief. For the present purposes, a "strain relief" is defined as means for connecting an electrical cable to an electrical device in such a way that the mechanical load on the cable is borne primarily if not exclusively by the insulation or sheathing of the cable rather than by the conductors therein. Referring to FIG. 9 herein, the typical 120 VAC tortuous path strain relief 198a in previous power boxes includes a series of spaced pegs 200a extending from one of the walls 202 of the power box base or cover. During assembly of the power box the 120 VAC cable 204 is woven through and around the pegs 200a, and the conductors within the 120 VAC cable 204 are connected to the primary coil of the step down transformer (not shown). The cable exits through an aperture 208 in one of the walls of the power box and terminates with a standard 120 VAC plug (not shown). Such a strain relief system usually passes the Underwriter's Laboratory (UL) cable pull test, which involves hanging a 35 pound weight from the 120 VAC cable 204 for one minute, but is less than ideal because it is so difficult and time consuming to weave the fairly stiff 120 VAC cable 204 through and around the strain relief pegs 200a.
As to the 12 VAC cable-to-power box connection, some prior power boxes have the 12 VAC cable preassembled with the power box at the factory, but this means that the entire power box/cable assembly has to be replaced or serviced if only the box or the cable is defective. Also, preassembling the 12 VAC cable to electrical components within the power box involves additional assembly steps which increase the cost of the unit. A prior art 12 VAC tortuous path strain relief 198b, with 12 VAC cable 210 woven to-and-fro through strain relief pegs 200b, is shown in FIG. 9. Other prior power boxes include terminal blocks (metal blocks which are female threaded to receive clamping screws) for the external 12 VAC connections. Terminal blocks are inconvenient and fairly costly, however.
Another problem with previous low voltage lighting system power boxes is that they are unnecessarily difficult to mount on a wall or other vertical surface near a 120 VAC outlet. Referring to FIGS. 9-11 herein, the typical existing mounting system includes a fairly small aperture 212 in the rear wall 202 (or an extension 214 thereof) of the power box with a short vertical slot 216 extending upwardly therefrom. The diameter of the aperture 212 is sized to be slightly larger than the head of a typical mounting screw and the width of the vertical slot 216 is sized to be slightly larger than the shank of the mounting screw but smaller than the head of the screw. Thus to hang the power box on the screw it is necessary to (i) vertically and horizontally align the aperture 212 in the rear wall of the power box with the head of the mounting screw; (ii) push the power box with the head of that the screw is received by the aperture 212; and (iii) release the power box so that the shank of the screw enters the vertical slot 216. Again, the problem with such a system lies in the initial alignment of the fairly small mounting aperture 212 (in the rear wall of the power box) with the mounting screw. Some power boxes, particularly those containing larger transformers, are quite heavy and it is inconvenient to try to achieve such an alignment while at the same supporting the heavy power box.
Still another problem with previous power boxes, more specifically the packaging (bases and covers) thereof, is that they are limited in terms of the electrical components, functions and lighting systems they can accommodate. For example, The Toro Company, assignee herein, previously had one base/cover combination for a 72 watt transformer (one suitable for powering 10 lights, each having a 7 watt bulb), with a manual switch; a second base/cover combination for a 72 watt transformer with a 4 hour/8 hour switch; and a third base/cover combination for a 118 watt transformer (for powering 16 lights, each having a 7 watt bulb) with a 4 hour/8 hour switch. There thus had to be a unique injection molding tool (or tool modification) for each unique base or cover. Also, the various bases and covers had to be carefully and separately inventoried to prevent problems on the assembly line.
The present invention addresses the aforementioned problems with previous power boxes. In particular, the present invention includes a power box having a superior tortuous path strain relief for the 120 VAC cable; a cost effective, easy-to-use method for achieving the 12 VAC connections; an improved technique for hanging the power box from a mounting screw or the like; and standardized packaging (base and cover) for accommodating a variety of electrical components, functions and lighting systems.